Arrangement for supplying local network emulation service over public connectionless ATM-network

ABSTRACT

An arrangement for supplying local network emulation services over a broad connectionless ATM-network. The ATM-network is in charge of connectionless data communication traffic by a broadband data service network. Private local networks can be connected to the ATM-network to exchange traffic with other local networks. The ATM-network emulates local networks so that the ATM-network can deal with the local network traffic. The broadband data service network includes servers which function as address resolvers for local network addresses and as local network relays for routing local network traffic via the ATM-network. The server uses unit specific addresses and local emulation groups as addresses.

BACKGROUND OF THE INVENTION

1. Field of the Invention

ATM (Asynchronous Transfer Mode) networks supply connectionless datacommunication traffic by means of BDS (Broadband Data Service). Privatelocal networks LAN (Local Area Networks) can be connected to the ATMnetwork for exchanging traffic with other local networks. The presentinvention relates to a modification of ATM networks in order to emulatelocal networks so the ATM network in a simple way can manage the localnetwork traffic, i.e. both public and private data communicationservices over ATM.

2. Discussion of the Background

According to previous technology one has been depending on the fact thatlocal network traffic first is analyzed in certain nodes in the ATMnetwork. This analysis is taking a lot of time as far as it results inan address solution, the result of which must be sent back to thecustomers in the local network, at which these themselves establishchannels to addressees. Consequently the ATM network only functions ascatalog for an address solution. A number of previous patent documentsrelate to this technology.

U.S. Pat. No.5,280,481 relates to a method and a device for making useof for instance MAC-protocol (Media Access Control) for communicationover an ISDN network (Integrated Services Digital Network). This iseffected by the ISDN network emulating a local network by converting itby means of the method and the device. The MAC addresses are managed inthe interface.

EP,A1 0 473 066 describes a system for interconnection of differentlocal networks via an ATM network. The connection is performed by meansof bridges which by means of internal tables decide the destinationaddress and by means of VCI (Virtual Channel Identifier) transmits theframe, which is divided into cells, through the ATM network.

U.S. Pat. No. 5.088.090 shows a system for the interconnection of localnetworks by means of bridges. The bridges, which detect whethertransparent routing or source routing is to be used, perform theconnection on MAC-level.

EP, Al 0 511 144 relates to a method and a device for connection oflocal networks to a WAN (Wide Area Network). The connection is performedby means of a so called concentration node in the local network, whichnode is used for making a network node interface towards the localnetwork, and an end node towards WAN with possibility of localaddressing.

The mentioned documents present different ways of connecting trafficbetween local networks and other networks, for instance ATM. In allcases different ways of managing the local addresses are treated.

SUMMARY OF THE INVENTION

In contrast to the previously known technology the nodes which receivethe local network traffic according to the invention act as both relaysand address dissolvers. The address solution constitutes a side effectof the relay's operation. By this the system according to the inventioncan rapidly transmit local network traffic through the network, at thesame time as it can tell the customers how they can chose alternativesignaling routes over the ATM-network for future traffic.

BRIEF DESCRIPTION OF THE DRAWINGS

According to the present invention an arrangement for local networkemulation service over public connectionless ATM data network issupplied. Local networks which want to communicate are connected to theATM network. The ATM network makes use of BDS for data transmission, atwhich servers attend to switching functions for routing and connectionof data traffic.

According to the present invention, servers function both as addressdissolvers for local network addresses and local network relays forrouting of the local network traffic.

The invention is presented in more details in enclosed patent claims.

SHORT DESCRIPTION OF THE FIGURES

The invention will now be described in details with reference to theenclosed figures, where

FIG. 1 schematically shows the construction of the networks,

FIG. 2 presents the relation between local addresses and BDS addresses,

FIG. 3 shows a routing table in BDS,

FIG. 4 presents a standard address structure,

FIG. 5 shows address structures for local network emulation according tothe invention,

FIG. 6 presents local network emulation layers,

FIG. 7 shows local network emulation routing and data bases according tothe invention,

FIGS. 8 and 9 presents protocol data units according to the invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

FIG. 1 shows the connection of a local network to an ATM network via aBDS network. The BDS network comprises BDS servers and BDS terminals.The BDS terminals also act as bridges to local networks. The localnetworks are preferably private and use the ATM network for datacommunication with each other. The ATM network is also used for publictraffic. The present invention relates to a modification of the ATMnetwork and especially the function of the BDS servers for simplifyingthe addressing and communication between the local networks.

We will first have a look at the relations between the addressingstructures in the local networks and in BDS. In local networksurroundings MAC addresses (Media Access Control) are practically alwaysused. These addresses have 48 bits and are uniquely associated to arespective unit, i.e. they do not reflect the network topology. Withinthe ATM network E164-addresses are used which have 64 bits and reflectthe network topology, like telephone numbers.

FIG. 2 is a chart which presents the relation between the addressingsystem. We can make the following observations.

For local network emulation end stations there is a direct equivalencebetween MAC-addresses and E164-addresses (for instance MAC^(a) toE164^(a))

For local network emulation stations which emulate MAC-layer bridgesthere can be more MAC addresses which form a unit in the BDS system (forinstance MAC^(d), MAC^(e) and MAC^(f) corresponding to E164^(d)). Thisdepends on the way the bridge wants to notify MAC addresses on the otherside (for instance MAC^(e) and MAC^(f)) for the local network emulationgroup.

MAC addresses may be regarded as pseudonyms for E164 addresses.

A local network emulation MAC address system indentifies a special localnetwork emulation group, and it is possible that a MAC address exists indifferent local network emulation groups, i.e that the MAC addressingsystems of local network groups are intersecting each other (this is notshown in FIG. 2).

Some units which are identified by the BDS system are not to be seenfrom the local network emulation system (for instance E164^(e) andE164^(f)). These units can be either BDS terminals which do not supplylocal network emulation services, or BDS servers.

There may be more systems for each of the system types in FIG. 2. Thisis to a great extent dependent on how the name giving and addressing isorganized and administered.

In the original BDS service, the routing was based on the combination<source-E164-address, destinations-E164-address> and the assumption thatall BDS terminals used one and only one BDS process. According to theinvention we now define the following for supporting the local networkemulation service in BDS: We are using the original BDS routing table asis shown in FIG. 3.

We use the combination <MAC,LEG> as pseudonyms for E164 addresses. LEG(LAN Emulation Group) are symbolic numbers which are used for relatingMAC- and E164 addresses to each other. An E164 address can have morepseudonyms, but a pseudonym can not exist for more than one E164address. This means that a station equipped with more ATM interfacesshould not register the same <MAC+LAG> on different interfaces, unlessit is not accepted that they are interfering with each other's routinginformation in servers.

For making the server able to distinguish between <E164> and <MAC,LEG>,the address codings of the original BDS scheme must be modified. Thiscan be performed by giving all addresses within the BDS system a tagspecifying the used address system. The new coding is described later.By establishing <MAC,LAG> pseudonyms to the original <E164> routingdatabases, BDS can be used for implementing local network emulationservices.

According to the invention the local network emulation service issupported over AAL5 (ATM Adaption Layer 5). It is then an advantage tomodify the BDS network in a way that some ISO/OSI configuration managingprotocols can be used.

Especially ISO9542 specifies a routing information exchange protocolbetween end systems (End Systems ES) and intermediate systems(Intermediate Systems IS) and ISO10589 specifies a similar informationexchange among intermediate systems. In the standards service accesspoints NSAP (Network Serviced Access Points) and points of attachmentsfor subnetwork SNPA (Subnetwork Points of Attachments) are defined. Inorder to make it possible to use ISO9542 for routing and configurationmanaging of BDS over AAL5, the sublayers have been somewhat modified sothe BDS protocol can be regarded as a layer 3c and AAL5 as a layer 3b.By that the selected ISO protocols can be used with very small or nochanges.

In a subnetwork a catalog function must exist in the routers so thatSNPA-points can be explicitly derived from NSAP addresses. In the BDSservice we presume a subnetwork of completely connected BDS-servers. Theonly translating address solution needed is the one where new logicalchannels VCI (Virtual Channel Identifier) are collected for a new<source E164, destination E164>.

A consequence of establishing relations between <E164> and <MAC,LEG> is,accordingly, the possibility to route on the basis of the latter in thepublic domain (even if <MAC,LAG> in the public domain are regarded asNSAP addresses, as explained below). One might even state that MACaddresses are the only perfect NSAP addresses so far defined, becauseMAC addresses have no relation whatsoever to underlying routingmechanisms.

According to the standardized addressing principles the relation betweenNSAP and SNPA can be one-to-one, one-to a multiple, or a multiple to amultiple. This relation is explicitly decided by a network addresscatalog function in systems where such translations are relevant. InISO8348 Addendum 2 network addressing is defined and specified in alldetails.

As is shown in FIG. 4 the NSAP address structure 1 5 consists ofmaximally 20 octets of two basic parts:

1. The initial domain part (IDP) and

2. The domain specific part (DSP)

The function of IDP is to specify a subdomain of the global network'saddressing subdomain, and to identify the authority which is responsiblefor allocation of network addresses in this specified subdomain. IDPconsists of two parts, AFI (Authority and Format Identifier) and IDI(Initial Domain Identifier).

In ISO8473 Addendum 2 is specified that the AFI values 00-09 arereserved and will not be assigned to specify a certain authority orformat. AFI values starting with the FIG. 0 are intended for specialcases, such as;

a change to another addressing scheme,

a technology for optimizing NSAP address coding;

a way to indicate that a field which normally would have kept a wholeNSAP address now keeps something less than a whole address, for instancea shortened form used for communication with a special subnetworkmilieu.

ISO8473 Addendum 2 consequently only reserves the AFI values 00-09 anddo not specify how they might be used. According to the invention theNSAP addresses are specified as shown in FIG. 5.

AFI=00 indicates a public connectionless data service user. Thefollowing two AFI values, 01 and 02, indicate alternative ways of usingMAC addresses over the BDS network. For AFI=01 is only used <MAC>;AFI=02 gives an NSAP address <MAC,E164>.

At each intermediate system the server examines the local networkemulation addresses to appoint next jump in the path to the goal endsystem and puts the SNPA address (VPI/VCI) for next intermediate systemin the VPI/VCI-field of the server cells. In order to find the suitablelogical path VPI (Virtual Path Identifier) is <MAC,LEG> used as apseudonym for an E164 table, where this information is available. In thestandard, address resolutions occur within the network address catalogfunction NADF (Network Address Directory Function) on the basis of bothdestination- and source addresses, as for the BDS-server.

The function of the E164 addresses from a configuration managing pointof view is somewhat more complicated, because they in BDS are regardedas NSAP addresses, whereas they outside BDS should be defined as SNPAaddresses. In the standard there are even a special NSAP addressstructure which is defined especially for managing E164 SNPA addresses.Since we in the BDS domain treat E164 addresses as NSAP addresses wecan, hovewer, use the standardized routing and configuration managingtechnology. This does not prevent that units in higher layers regardthis address as a basis for deriving any SNPA addresses.

The local network emulation layer at end stations and bridges equippedwith ATM-interface is shown in FIG. 6. There are two possible ways oftransferring data from MAC service interface. One is to use signalledlogical channels SVC (Signalled Virtual Circuits), and the other is touse the BDS-service. For signalled logical channels a connection isestablished and data is tranferred by use of AAL5. For BDS no connectionmanaging is required from the local network emulation layer's point ofview,

LAN emulation stations and end stations need to maintain the followingconfiguration information, as is shown in FIG. 7.

1. Destination addresses, which are indexed with the combination<destination-MAC-address, destination -LAN-emulation group>. The E164address is for signalled logical channels. If no channel is established,and the it communication accordingly occurs through the BDS server,normal-VPI is ="BDS".

2. Source-groups, which hold information about local network emulationgroups at which the local network emulation station is registered. Thisinformation, the use of which is a local matter, is maintained by ESHprotocol data units ESH PDU (End System Hallo Protocol Data Unit) fromthe server.

3. BDS server destination addresses, which consist of servers which areavailable for local network emulation over ATIM. The choice of servermight be based on different service quality values QOS (Quality ofService) and might be defined as a part of the initial phase for logicallocal network stations which have signalling ability. The informationabout available servers are obtained outside the band (for instance byexplicitly configuring host data bases at the stations).

In FIG. 7 are also shown BDS server databases, which take bi-directed,semi-permanent logical paths to local network emulation stations and toother servers. The databases are:

1. Local destination addresses, which are indexed by the combination<destination-MAC-address, local network emulation group>. The tablecontains routing information about local network emulation stationswhich are served by this server. Notice that it is not necessary thatthe logical channel identifiers VPI at this data base must be BDS if theserver is implemented as a real overlaying BDS network, since thelogical path should need to be over a logic channelswitch/cross-connection.

2. Destination addresses level 1, which are indexed as the former.E164-addresses are to local network emulation stations and not to otherBDS servers.

3. Destination addresses level 2, which are indexed by <local networkemulation group>.

When a local network emulation end station is connected to a switch, itwill register itself to its normal server by means of an ESH (End SystemHello) protocol data unit PDU to this server. This ESH PDU is sent backto the transmitting local network emulation managing unit by aconfiguration message function (in accordance to ISO9542) at the server,which quite simply sends ESH PDU back to the specifically addressedMAC/E164 local network emulation end station.

ESH protocol data units are constructed as follow: The SAL indicator(Segment and Reassembly Layer) for this MAC-address must be 16, so theSA-field contains a combination <AFI/IDI=02+MAC-address, local networkemulation group number> corresponding to the local network emulation endstation. The original E164-address which indicates port- and switchidentity at the virtual local network station and nothing else, isexclusively derived by the server by its knowledge from which localchannel the ESH protocol data unit originated.

According to FIG. 8 we presuppose 8 octets for representing groupnumbers. This is in line with the E164 group number scheme. Name givingconventions for logical local networks might be in accordance withInternet, for instance A.B.C.D.E.F.G.H.

ESH protocol data units can be transferred in one out of two differentways, but always direct on AAL5 over reserved logical subchannels(VCI=9542).

The local network emulation managing unit constructs an ESH protocoldata unit, which is sufficiently small for fitting on one single cell(inclusive AAL5 trailer). The available payload in a one cell AAL5protocol data unit is 40 octets (53 -5 -CRC32-check length=40).

The local network emulation managing unit transmits it via AAL5-messageswhich are longer than one cell (for instance in the case with moresource adresses/local network emulation groups).

The first method is preferred in order to minimize the processing inservers and should give a F-flow mechanism for the local networkemulation service over BDS. This F-flow mechanism will now be called"F-LAN".

If the local network emulation end station represents a bridge, forinstance to an Ethernet, it can also wish to register more MAC addresseson its E164-address, for instance for each new MAC-address which isregistered by the bridge for the Ethernet side a new ESH protocol dataunit shall be tranferred by the local network emulation layerconfiguration unit to the ATM-side, if the F-LAN-mechanism is used,otherwise a longer AAL5-packet can be used for the same purpose, but inan AAL5-piece.

As a result of the ESH protocol data unit the server registers thefollowing information in its local database: <E164 MAC-address, localnetwork group>. All database posts in servers which contain E164 addressposts originating from local network emulation end stations areconsequently equipped with references to emulated local networks towhich they belong, as references to MAC addresses are associated withthe E164 address. If a local network emulation station belongs to morethan one virtual local network, it will be registered twice in the localrouting database, because the registration is made per NAP, which isdefined as a combination <MAC-address+local network emulation group>.

Each local network emulation end station reports continuously, with afrequency decided by a configuration clock in ISO9542-units, about itsaccessibility to the normal server.

Whenever a server registers a new post in its local database, it willissue a configuration message to other servers. This is also performedby means of an ESH protocol data unit as above, but with certainmodifications.

The address resolution occurs as a side-effect according to thefollowing. When resolution of a MAC-address to an E164-address occurs inservers, the server sends back a redirect protocol data unit RD PDU(Redict PDU) with the result to the initiating local network emulationend station. The redirect protocol data unit is shown in FIG. 8 with thefollowing interpretation: "Destination address" is<MAC+LEG>(alternatively only the MAC-address need to be specified, i.e.AFI/IDI=01) and "sub network address" is the E164-address which can beused for establishing a signalled logical subchannel. Notice that inthis case the E164-address is used for deriving an SNPA-address by whichthe signalled logical subchannel is established.

Alternatively the local network station which receives the redirectprotocol data unit can use the E164-address over the BDS-system, withoutlocal network emulation, i.e. by composing an NSAP-address<(AFI/IDI=00)+E164> out of the received SNPA E164-address.

For this redirect protocol data unit the additional selection field isset to the octet 1=100 0011 (QOS in accordance with ISO8473) and theoctet 2=01 (source address specific QOS in accordance with ISO 8473) 000001 (MAC-address resolved).

The size of the redirect protocol data unit is 40, i.e. it fits in theF-LAN-mechanisms.

At jamming in the BDS-network the server issues, as a counteractionmeans, redirect protocol data units to the local network emulation endstations and strongly recommends that they establish signalled logicalchannels to goal local network emulation stations or groups of endstations (see FIG. 8). For this protocol data unit the additionalselection field is set to octet 1 =1100 0011 as above, and the octet2=0100 0010 ("Establish logical channel to E164").

At transmission of data the local network emulation unit has twochoices: Either it will use a signalled logical subchannel to the goallocal network end station, or, if no logical channel is found, it willuse the BDS-service with its implicated VPI=BDS. The local networkemulation end station can combine use of the BDS-service with theestablishing of a signalled logical channnel parallelly.

Examples of Initiation, Registration, Address Solution, ConnectionManaging and Data Transmission

Charging time and new registrations of MAC-addresses or local networkemulation groups (ISO09542-protocol data units over AA15, with VPI=BDS,VCI=9542).

1. Station - - - AAL5^(VCI=9542) ESH PDU {(MAC+LEG)^(NSAP), E164^(NSAP)} → server. "I am here, please register my MAC-addresses and localnetwork emulation groups".

This mechanism supposes that the server in some way can derive theE164-address from which the ESH protocol data unit originates.

2. Server - - - AAL5^(VCI=9542) ESH PDU {(MAC+LEG)^(NSAP), E164^(NSAP) }→ station.

Configuration message, i.e. "it is OK, the server has registered you".

3. Server - - - AAL5^(VCI=9543) ESH PDU {(MAC+LEG)^(NSAP), E164^(NSAP) }→ other servers.

Configuration message: "I route the following stations locally".

Notice that ESH which is sent back to other servers might be labelledVCI⁹⁵⁴³ so the receivers are informed about that this information isintended for globally routing data bases. This server would yet be ableto compile this information from the data base in FIG. 7, but thissolution is more effective. It is the task of the server to decidewhether this configuration information through VCI⁹⁵⁴² and VCI⁹⁵⁴³should be distributed to relevant local network emulation units or not.This can be regarded as something which shall be decided byconfiguration message functions of servers.

Continuity

1. Station - - - AAL5^(VCI=9542) ESH PDU {(MAC+LEG)^(NSAP) } → server."I am still here".

2. Server - - - AAL5^(VCI=9542) ESH PDU {(MAC+LEG)^(NSAP), E164^(NSAP) }→ station. "You are still registered in the following groups" (of thelocal server).

Datatransmission

1. Station - - - BDS UNITDATA {source (MAC+LEG)^(NSAP), destination(MAC+LEG)^(NSAP), data QOS} → server.

Server: Address resolution (local, global based either on destinationMAC or on LEG)+forwarding data.

2. Server - - - AAL5^(VCI=9542) RD PDU {(MAC+LEG)^(NSAP) }, additionalselection field octet nr 1=1100011, i.e. "QOS", octet nr 2=01 "sourceaddress specific QOS"+00 0001 "MAC-address resolved") → station.

"I have just resolved the destination MAC-address of the followingE164-address. If you want to, use it to establish a signalled logicalsubchannel to this E164-address".

Notice that this message should be sent between servers and localterminals, not between servers. The server which transmits the messageshould adapt the redirect protocol data units to the data base of thelocal stations.

Contra pressure from the server to local units.

1. Server - - - AAL5^(VCI=9542) RD PDU {(MAC+LEG+E164}, additional fieldoctet nr 1=1100011, octet nr 2=0100 0001 "Establish signalled logicalsubchannel to E164") → station.

"You had better start using a signalled logical subchannel for thisE164-address".

This counter pressure mechanism can only be used locally by servers forrouting stations.

ARP-mechnisms.

For polling servers the station transmits an empty BDS. The closestserver transmits automatically a redirect protocol data unit to thestation which produced the inquiry. This redirect protocol data unit ofcourse contains information about the E164-address to the specifieddestination-MAC-address.

1. Station - - - BDS {Source(MAC+LEG)^(NSAP), destination(MAC+LEG)^(NSAP). No data} → server.

2. Server - - - AAL5^(VCI=9542) RD PDU {(MAC+LEG)^(NSAP) } → station.

Configuration message "as a result of the inquiry".

The station which receives the message can store (MAC+LEG)^(NSAP).

The enquiring mechanism above only applies to level 1.

The present invention accordingly offers the following advantages.

BDS is used as an underlying connectionless broad band data service.

The function of the local network emulation end stations is simplified.

The server is used as a data relay, as name resolver (MAC-addresses toE164-addresses) and as configuration manager for local network emulationservices.

Within the BDS subnetwork MAC-addresses are treated as network addressesand MAC-addresses+local network emulation group numbers asNSAP-addresses.

The local network emulation group addressing will be as like theE164-addressing as is possible, so it will be easier to use themtogether.

Many of the already known configuration managing protocols, for instanceISO9542 and ISO10589 can be used for minimizing duplication of work andminimizing logical errors.

We claim:
 1. Arrangement for supplying local network emulation serviceover public connectionless ATM-network comprising BDS-service for datatransmission and local network LAN connected to the ATM-network, whereinBDS-servers are in charge of switching functions for routing andcarrying traffic and act as address resolvers for local networkaddresses and as local network relays for routing of the local networktraffic via the ATM-network, wherein the server forms particular localnetwork addresses comprising unit specific addresses and local emulationgroup number as an address in the BDS-service, which local emulationgroup number relate the unit specific addresses and the ATM-addresses toeach other, wherein the servers can use the local network addresses inparallel with the normal ATM-addresses.
 2. Arrangement according toclaim 1, wherein the local network addresses and the normalATM-addresses are separated by a tag, by means of AFI-values in ISO8473addendum
 2. 3. Arrangement according to claim 2, wherein within theBDS-subnetwork it deals with MAC-addresses as network addresses andMAC-addresses+local network emulation group numbers as NSAP-addresses.4. Arrangement according to claim 1, wherein standardized configurationprotocols are used.
 5. Arrangement according to any of the previousclaims, characterized in that the servers are distributing addressing-and configuration information in the network at connection of localnetworks via a BDS-terminal.
 6. Arrangement according to claim 2,wherein standardized configuration protocols are used.
 7. Arrangementaccording to claim 3, wherein standardized configuration protocols areused.
 8. Arrangement according to claim 2, wherein the servers aredistributing addressing- and configuration information in the network atconnection of local networks via a BDS-terminal.
 9. Arrangementaccording to claim 3, wherein the servers are distributing addressing-and configuration information in the network at connection of localnetworks via a BDS-terminal.
 10. Arrangement according to claim 4,wherein the servers are distributing addressing- and configurationinformation in the network at connection of local networks via aBDS-terminal.
 11. Arrangement according to claim 6, wherein the serversare distributing addressing- and configuration information in thenetwork at connection of local networks via a BDS-terminal. 12.Arrangement according to claim 7, wherein the servers are distributingaddressing- and configuration information in the network at connectionof local networks via a BDS-terminal.
 13. Arrangement according to claim4, wherein the standardized configuration is an ISO9542 standardizedconfiguration.
 14. Arrangement according to claim 4, wherein thestandardized configuration is an ISO10589 standardized configuration.15. Arrangement according to claim 6, wherein the standardizedconfiguration is an ISO9542 standardized configuration.
 16. Arrangementaccording to claim 6, wherein the standardized configuration is anISO10589 standardized configuration.
 17. Arrangement according to claim7, wherein the standardized configuration is an ISO9542 standardizedconfiguration.
 18. Arrangement according to claim 7, wherein thestandardized configuration is an ISO10589 standardized configuration.